General purpose controllers are increasingly being used in testing applications. Controllers may be analog devices, but due to the increasingly complex and precise control algorithms required, digital controllers (for example microprocessor-based) are being used.
In the field of testing applications for engines, for example, testing systems are used for controlling an operating characteristic of the engine and an operating characteristic of a dynamometer connected to the engine. Operating characteristics of both the engine and the dynamometer may be controlled. In some situations, a transmission with a plurality of gear ratios is coupled to and between the engine and dynamometer. Operating characteristics that may be controlled include engine speed, engine torque, throttle position, dynamometer torque, dynamometer speed, and dynamometer current. Typically, one engine characteristic and one dynamometer characteristic are being simultaneously controlled.
If there is not a transmission, a coupling mechanism provides a direct connection between the engine and the dynamometer. The engine and transmission speed are substantially equal. The engine output speed and the dynamometer input speed are also substantially the same. Obviously, engine speed and dynamometer speed can not be controlled simultaneously and neither can engine torque and dynamometer torque. Therefore the list of operating conditions that may be controlled include engine speed, engine torque, throttle position, and dynamometer current.
Most systems include analog controllers. That is, the engine's throttle and the dynamometer are controlled by analog components. Such systems are sold under the registered trademark Cellmate by Digalog of Ventura CA. Analog controllers do not allow for instantaneous changes from one mode to another mode, for example, engine speed to engine torque. The Cellmate system for example must be brought down to 0% throttle (IDLE) and all the load must be taken off of the dynamometer before a mode change occurs.
It is therefore desirous to provide a test controller that allows for instantaneous mode changes.
A test is usually a series or cycle of steps. For example, a series of steps might include:
(1) HOLD IN LOW IDLE FOR 5 MINUTES, PA1 (2) RAMP UP TO AN ENGINE SPEED OF 2100 RPM WITH NO LOAD ON THE DYNAMOMETER, AND PA1 (3) STEP DOWN TO LOW IDLE.
The system must be programmed to accomplish this cycle. An operator typically has to write a "program" or a series of steps in order to set up a cycle. The system usually includes a display and a keyboard for inputting data.
A problem with this type of arrangement is that an operator must be familiar with the "language" that is used to program the system. The operator must be extensively trained in order to operate or program the system.
Another problem associated with past systems relates to the inherent dynamic aspects of an engine's response. Typically, these systems control the engine using a feedback control scheme. Furthermore, the control scheme may include proportion-plus intehral-plus derivative control. However, it has been discovered that the response of some engines include a dynamic aspect which make the engine's response harder to predict utilizing the typical control strategies.
The present invention is adapted to overcome one or more of the problems as set forth above.